The present invention relates to data networking and more particularly, to systems and methods for efficiently transporting Fibre Channel frames over a SONET/SDH transport network.
SONET/SDH and optical fiber have emerged as significant technologies for building large scale, high speed, Internet Protocol (IP) based networks. SONET, an acronym for Synchronous Optical Network, and SDH, an acronym for Synchronous Digital Hierarchy, are a set of related standards for synchronous data transmission over fiber optic networks. SONET/SDH is currently used in networks spanning large areas, such as metropolitan area networks (MAN) and even wide area networks (WAN). A SONET/SDH system consists of switches, multiplexers, and repeaters, all connected by fiber. The connection between a source and destination is called a path.
One network architecture for the high-speed interconnection of computer devices in network communication is Fibre Channel, the core standard of which is described in ANSI (American National Standards Institute) X3.230-1994. Arising out of data storage requirements, Fibre Channel currently provides for bi-directional gigabit-per-second transport over communication networks in Fibre Channel frames that consist of standardized sets of bits used to carry data over the network system. The high-speed Fibre Channel links are limited to no more than 10 kilometers.
It is advantageous to “combine” the SONET/SDH and Fibre Channel technologies, and new standards and protocols have emerged. For example, it is sometimes desirable to link two or more SANs (Storage Area Networks), which operate with Fibre Channel protocol, over a MAN (Metropolitan Area Network), or even a WAN (Wide Area Network), which typically operates under SONET or SDH standards. This extension of Fibre Channel from 100 kilometers to over several hundred, or even thousand, kilometers, is made by mapping Fibre Channel ports to a SONET/SDH path for transport across a SONET/SDH network.
Generic Framing Procedure (GFP) defines the mapping for the transport of higher level protocol client data over SONET/SDH networks. GFP specifically provides for transparent GFP (GFP-T) to encapsulate Fibre Channel (and certain other protocols, such as Gigabit Ethernet) client data frames into GFP-T frames and then to map the GFP-T frames into SONET/SDH frames for transport across the SONET/SDH network. As defined by the ITU-T G.7041 GFP standard, rather than storing an entire Fibre Channel frame, the individual characters, both data and control (including idle) characters, of the Fibre Channel frame are demapped from 8B/10B block code and then mapped into periodic, fixed length GFP frames. GFP-T has a resulting low transmission latency in accord with the high-speed nature of Fibre Channel. However, in exchange for low transmission latency (and hence high-speed transmission), GFP-T requires that the transport channel capacity be at least as large as the incoming data (and control signal) rate for the Fibre Channel characters to be encoded. Even in lightly loaded applications, GFP-T mapping transports the entire Fibre Channel physical link, including all of the interframe idles, and even adding padding characters into a GFP frame so that the frame can be transmitted quickly. Hence GFP-T requires full rate transport bandwidth.
This is a problem for telecommunication applications where long-distance connections are costly. A not uncommon telecommunication practice is to oversubscribe the transport link. For example, an OC48 pipe (a SONET/SDH link having a capacity of 2.488 Gigabits per second) might be used to handle four GE (Gigabit Ethernet) streams by taking advantage of statistical multiplexing, i.e., not all GE streams burst communication packets all the time. But GFP-T is not used because GFP-T is antagonistic toward oversubscription of the transport link. As explained above, GFP-T requires that the transport channel capacity should be at least as large as the incoming data and control signal rate, i.e., there can be no oversubscription of the SONET/SDH transport network.
GFP does provide for frame-mode GFP (GFP-F) transport in which the client data protocol units, i.e., frames, are adapted for transmission over the OTN (Optical Transport Network). For example, standard Ethernet, in contrast to Fibre Channel which is accommodated by the block-code oriented GFP-T, is provided for by GFP-F. If one tries to use Fibre Channel over GFP-F by following standard Ethernet over GFP-F procedures, one complete Fibre Channel frame or Ordered Set is mapped into one GFP frame. Since each GFP-F frame has a fixed overhead of 16 bytes, the overhead percentage is prohibitively high for smaller frames and Ordered Sets. In other words, Fibre Channel over conventional GFP-F is not effective for an oversubscribed SONET/SDH transport network.
Therefore, a way of providing for the transport of Fibre Channel frames across an oversubscribed OTN transport path, such as SONET/SDH, is highly desirable. To use bandwidth efficiently, multiple Fibre Channel Ordered Sets and frames should be capable of being mixed in one GFP payload area.